1. Field of the Invention
One or more aspects of the present invention relate to improved water-soluble fertilizer (“WSF”) compositions. More particularly, they relate to solid fertilizer compositions having rapid dissolution times and high water-solubility, wherein the WSF compositions also provide stable, precipitate free stock and feed solutions and excellent dry-storage characteristics. One or more aspects of the present invention also relate to methods of using improved WSF compositions.
2. Background and Description of Related Art
Carbon, hydrogen, oxygen, nitrogen phosphorus, potassium, and sulfur are the primary elements essential to all life. Soils contain all of these elements in addition to other macro and micronutrients which are needed for plant growth. Typically, such elements are not present in the soil in sufficient quantity or in forms that can support maximum plant growth and yield. In order to overcome these deficiencies, fertilizers having specific chemical constituents in specific amounts are often added to the soil, thereby enriching the growth medium. The fertilizers may be supplemented with certain trace elements such as copper, iron, manganese, zinc, cobalt, molybdenum (typically as a molybdate), and boron (typically as a borate), as oxides or salts.
Fertilizer compositions can be provided in many forms including dry granulated or free-flowing compositions intended. For dispersion or for dissolution in aqueous solution prior to delivery to plants or crops. Advantageous, dry fertilizer compositions provide for quick release (high water-solubility) when production of stock solution is desired. In other contexts, dry fertilizer compositions are advantageous when they provide for slow release (as by low water-solubility or by encapsulation), such as when the steady or controlled delivery of nutrients over time is desired.
In greenhouses, nurseries and other intensive horticulture environments, best plant growth results are achieved when macro and micro nutrients are carefully and thoroughly delivered to the growing plants. Many plant and agricultural growers choose to utilize water-soluble fertilizers for accomplishing this result. Typically, such fertilizers are formulated as solids which may be dissolved by the user to prepare concentrated stock solutions which are subsequently diluted into irrigation water employing proportioners or injection devices, thereby forming so called “feed solutions.”
Agricultural fertilizers usually contain a select number of macronutrients. Agricultural fertilizers are typically intended to be applied infrequently and normally prior to or alongside seeding. Examples of agricultural fertilizers are granular triple superphosphate, potassium chloride, urea, ammonium sulfate, and anhydrous ammonia. By comparison, horticultural or specialty fertilizers, on the other hand, are formulated from many of the same compounds as agricultural fertilizers and some others to produce well-balanced fertilizers that also contain micronutrients.
Typical dry WSF compositions are made by mixing different nutrient containing powders and/or granules. In general the pH of the final solution sprayed or applied by irrigation is around 6-6.5. For soft water like most rain water, the WSF composition should yield a pH of close to the desired pH after dissolution and dilution. For hard water, the WSF compositions tend to be more acidic to neutralize the higher pH of the water. Therefor for soft water and general purpose products, the ingredients consist from a group of ‘neutral’ nutrients. These ingredients give a close to neutral pH in a concentration range from about 1-10%. For hard water products, an acidic component like urea phosphate may be added.
It is important to formulate these high analysis fertilizer compositions so that they dissolve quickly and completely with no precipitation. Solubilities of about 200 grams/L are considered high and are advantageous. Furthermore, these fertilizer compositions must provide good long-term stability in both dry-form and in stock solutions. For example, compositions which cake, crust, agglomerate, or decompose decrease the suitability of the fertilizer composition.
A drawback of many prior art “water-soluble” fertilizers is that they tend to “cake.” Caking interferes with their handling in bulk by the producer and by the end user and may interfere with the speed of dissolution of the fertilizer in water. Fertilizer caking is believed to be caused by several factors, e.g., the formation of crystalline bridges to which solid connections are formed at the points of contact among the granules. Alternatively, there may be capillary adhesion or bonding between the granules with significant force often being necessary to break this adhesion or bonding. The cohesive forces will vary depending upon the storage conditions and other variables such as the nature of the composition. The hygroscopic nature of many fertilizers may also results in undesirable caking. Further, hygroscopic compounds provide a medium—via absorption of water—whereby undesirable chemical reactions may occur. In all cases, however, the caking causes a serious problem to which a completely satisfactory solution has long been lacking. Additives are often added to attempt to inhibit caking. For example, U.S. Pat. No. 5,286,272 describes an inorganic fertilizer composition that flows freely and resists caking comprising a beneficial agent and a separate anti-caking agent (tripotassium phosphate).
Other prior art methods proposing to decrease fertilizer caking also involve the use of additives to the fertilizer composition. Typical additives include the use of finely divided powders which must cover the fertilizer substantially uniformly such as for example talc, kaolin and diatomaceous earth. Surfactants may also be used. Further additives include compounds that also tend to form a hydrophobic film around the fertilizer granules such as paraffin wax, polyolefin wax and mineral oils. These formulations, which may demonstrate some improved storage characteristics, are often not suitable for the preparation of stock or feed solutions because they may result in suspensions in solution containing these agents. Undissolved particulates can result in undesired clogging of the feed line, proportioner, or sprayer.
Accordingly, advantageous WSF compositions should be readily soluble in aqueous solutions, providing a completely substantially completely dissolved solution shortly after mixing, thereby allowing prompt use of the stock or feed solution. Again, once dissolved in solution, precipitates (or non-dissolved compounds) in the stock solutions can cause clogging of the proportioners and irrigation lines. Therefore, WSF compositions should also remain dissolved once in solution at varying concentrations (from concentrated such as in a stock solution to dilute such as in a feed solution). Further, water-soluble fertilizer compositions which release non-trivial amounts of gas are usually not suitable for use in tanks, containers, on large agricultural scales, or for use in sprayers, drippers, and irrigation lines. Accordingly, water-soluble fertilizer compositions should not release significant gases during dissolution: preferably, they should release close to none.
An additional functional requirement for advantageous fertilizer compositions is the ability to store large amounts of fertilizer in containers such as bags without decomposition or the production of gas. Also, formulations which can be manufactured by simply mixing one or more of the ingredients without intermediate wetting or drying stages are also idea.
These functional requirements for water-soluble fertilizer compositions of this variety have presented ongoing problems for producers and developers of such products and these problems have not been fully solved by previously available fertilizer compositions. Most prior art references attempt to address this issue via modifications of the proportioners or sprayer. For example, U.S. Pat. No. 6,866,780 describes a heated ultrasonic treating device comprising a sump through which suspended matter-containing liquid passes, a temperature-controllable heater and a ultrasonic vibrator disposed in the sump which function to “pulverize” the suspended matter upon heating/vibration. Other attempted solutions include U.S. Pat. No. 6,200,928, which describes “effervescent preparations” for plants comprising generally non-nutritive carbonates, non-nutritive water-soluble acids, and various nutrients such as methionine. A distinct disadvantage of effervescent compositions is that while production of gas and the resulting agitation increase dissolution speed, they also create a hazard when used in closed or unvented containers. Additionally, there are limited numbers of nutritive carbonate or gas producing fertilizers suitable for creation of effervescent formulations and non-nutritive carbonate sources effectively dilute the nutritive content of the composition.
U.S. Pat. No. 6,312,493 describes water-soluble fertilizer compositions containing phosphate free organic acids to aid solubility and one or more fertilizer components. Another soluble fertilizer composition is described in U.S. Pat. App. No. 2006/0243012. The soluble fertilizer composition comprises calcium and/or magnesium phosphates. In attempting to overcome the poor physical properties of monobasic calcium phosphate (MCP) and monobasic magnesium phosphate (MMgP) fertilizers (slight solubility in water), the inventors modify these compounds by chemical reaction to provide fertilizer formulations comprising 1) calcium phosphate or magnesium phosphate; 2) at least one alkali metal phosphate such as monopotassium phosphate; and 3) phosphoric acid (PA). In formulating these compositions, certain embodiments describe the mixing of phosphoric acid, monopotassium phosphate, and various alkali hydroxides in water; reaction of the components; and subsequent drying to form a final composition having an acidic pH. Improved solubility is obtained by modification of the initial chemical constituents into compounds with improved solubility characteristics.
Another exemplary soluble fertilizer composition which attempts to provide improved solubility characteristics is U.S. Pat. No. 6,826,866. This patent describes the use of dilute, aqueous water-soluble fertilizer compositions containing a surfactant system comprising water-soluble nonionic surfactant and alkyl polyglycoside in a weight ratio of from 2:1 to 1:1.
A classical water-soluble fertilizer composition is described in U.S. Pat. No. 4,175,943 where a water-soluble mixed fertilizer composition in solid form and a method of producing the fertilizer composition is described. The fertilizer comprises a mixture of urea, phosphoric acid and at least one potassium salt selected from the class comprising potassium sulfate, potassium nitrate and potassium chloride. Ammonium salts selected from the class comprising ammonium nitrate and ammonium sulfate may optionally also be added to the mixtures.
Other typical prior art formulations which intend to improve the solubility of certain compounds, such as trace metals, may also utilize either chelating agents or adjustment of the final composition to an acidic pH when in solution.
The above prior art formulations suffer from one or more disadvantageous properties including: (1) poor solubility of one or more nutrients or additives in solution; (2) the need for undesirable additives to aid dissolution or to impart anti-caking properties; (3) slow dissolution times; (4) precipitation of nutrients or additives from solution (resulting in clogging or other malfunction of, for example, a nutrient proportioner); (5) prolonged, difficult, or expensive compounding steps; (6) evolution of gas; and/or (7) chemical safety and stability issues including decomposition of the dry or dissolved fertilizer mixture. Accordingly, there has been a long-felt need for compositions which remedy the deficiencies of prior fertilizer compositions.